The present invention is directed to a dental X-ray diagnostic device for producing panoramic layer exposures of the subject particularly of a jaw. The device comprises an X-ray source which is mounted on a rotating arm of a carriage, a cassette which accepts the X-ray film and is mounted to rotate on the arm so that the film is moved during an exposure as the arm rotates both the source and cassette around the subject and a slit diaphragm disposed in the beam path between the source and the subject for limiting the width of the beam of radiation projected from the source.
A dental X-ray diagnostic device for producing panoramic layer exposures of a subject such as a jaw of a patient are known and have been sold. An example is disclosed in a Siemens brochure entitled ORTHOPANTOMOGRAPH No. MD 80/1238. As disclosed in this brochure, the diagnostic device provides a panoramic layer exposure or a panograph of a jaw as the patient's skull is fixed in a special support mount and the device has a mechanism which rotates the X-ray tube and the cassette containing the film around the patient so that the entire jaw can be imaged on the film with a single exposure. The image gained with this device is a layered image which is only sharp for the subject at a very specific layer depth while the zones adjacent the specific depth are blurred. The thickness of the sharply imaged zone is thereby proportional to the radius of curvature of the layer form and inversely proportional to the slit width of the X-ray beam. In the known devices which have a constant slit width over the entire motion sequence, the so-called normal layer, which comprises the jaw area including the front teeth, has a different layer thickness because of the different curvatures of the patient's jaw.
In order to achieve an appropriate radiation intensity for the entire area to be imaged without those areas for which such an intensity is not required being overloaded radiation-wise, it is known from German OS No. 2,753,119 to design a diaphragm which is positioned between the radiation source and the subject to be exposed with a wedge-shaped slit which converges downward. With the assistance of such a wedge-shaped slit diaphragm, the intensity of the radiation is greater in the upper area of the jaw than in the lower area. Thus, differing layer thicknesses of the subject in the vertical plane can be taken into consideration but the X-ray beam remains constant as viewed over the entire exposure of the jaw.
Due to the tighter curvature of the jaw in the area of the front teeth, a lower layer thickness is present there. This provides disadvantages particularly given subjects whose jaws depart from the normal shape. For example, if the dentitions with teeth are extremely slanted or with projecting canine, the images of these slanted teeth or projecting canines will not always have sufficient sharpness.